1. Field of the Invention
Embodiments of the present invention relate generally to a detection and decontamination system and method. More specifically, embodiments of the present invention relate to a system and method for rapidly and accurately detecting, characterizing, quantifying, and decontaminating organics present in the atmosphere due to chemical and/or biological spills, weapons, terrorist attack and/or other releases.
2. Background of the Invention
In the event of a chemical and/or biological spill, weapon, terrorist attack and/or release, rapid detection, characterization, quantification, and decontamination is crucial. Commercially available sensors and sensing technologies provide for detecting contaminants on the surface of an object. However, these sensors and technologies generally require collecting a sample of the contaminant which must then be transported to a remote instrument for contaminant identification and concentration determination.
Photocatalytic agents are effective for removing organic pollutants in both aqueous and gaseous environments. Heterogeneous semiconductor photocatalysis relies upon photoactive semiconductors, such as titanium dioxide (TiO2) for example, to not only sorb noxious and pollutant gaseous emissions, but to photocatalytically oxidize or reduce such emissions into less toxic organics and carbon dioxide.
As illustrated in Equation 1 below, when TiO2 is illuminated by light having energy hv equal to or exceeding the TiO2's bandgap energy (3.2 electron volts for anatase TiO2), electrons (e−) are excited (promoted) into the conduction band. Electron promotion creates positive holes (h+) in the valence band. If these electron-hole pairs do not recombine to produce heat (as illustrated in Equation 2 below), the pairs promote oxidative and reductive electron transfers as shown in Equations 3 through 7 (adapted from Chemical Engineering Science, Vol. 56, 1561 [2001]).TiO2+hv→TiO2(h++e−) electron-hole pair formation  Eq. 1e−+h+→heat recombination  Eq. 2e−+Mn+→Mn(n−1)+ reduction  Eq. 3h++H2O(ads).OH+H+ oxidation of adsorbed (abs) water  Eq. 4h++2OH(ads)−→.OH+OH− oxidation of adsorbed hydroxide ions  Eq. 5.OH+R(ads)→.R(ads)+H2O organic oxidation  Eq. 6.R+(.OH,.Rads)→products termination  Eq. 7                where hv=light energy, h+=positive holes, e−=electrons, Mn+=oxidized compound and R(abs)=the absorbed organic species or moiety.        
The charges in the valence and conduction bands can oxidize and reduce moieties at the TiO2 surface. In addition, the positive holes often react with water or hydroxyl ions sorbed to TiO2, producing hydroxide radicals which, in turn, oxidize absorbed organic moieties.
TiO2 has been found to be an effective oxygen sensor, since the oxygen diffuses into TiO2 oxygen vacancies, thus increasing the TiO2 resistivity. This is especially true at elevated temperatures. See, for example, A. Rothschild, et al. “Sensing Behavior of TiO2 Thin Films Exposed to Air at Low Temperatures,” Sensors and Actuators B, Vol. 67, 282 (2000); R. K. Sharma, et al., “Influence of Doping on Sensitivity and Response Time of TiO2 Oxygen Gas Sensor,” Review of Scientific Instruments, Vol. 71, 1500 (2000); and N. Golego, et al., “Sensor Photoresponse of Thin-Film Oxides of Zinc and Titanium to Oxygen Gas,” J. Electrochem. Soc., Vol. 147, 1592 (2000).
TiO2 thin films have been used, at elevated temperatures (100° C. to 500° C.), to detect different types of alcohols including ethanol, methanol and propanol. See, for example, G. Sbeerveglieri, et al., “Titanium Dioxide Thin Films Prepared for Alcohol Microsensor Applications,” Sensors and Actuators B, Vol. 66, 139 (2000).
Resistivity changes occur when gases chemisorb onto the TiO2 surface. Such resistivity changes have been used to derive current, phase lag, and surface potential interactions, producing one-point relationships unique to the individual compounds sorbed onto the TiO2. See, for example, M. R. Islam, et al., “Chemical Sensor Based on Titanium Dioxide Thick Film: Enhancement of Selectivity by Surface Coating,” Appl. Surface Sci., Vol. 142, 262 (1999).
The chemisorption of compounds onto the TiO2 surface has also been used to capture distinct responses from applied sinusoidal voltages on rutile TiO2 films in the presence of various organic gases. These responses were enhanced in the presence of 700 nanometer (nm) light. See, for example, N. Kumazawa, et al., “Photoresponse of a Titanium Dioxide Chemical Sensor,” J. Electro. Chemistry, Vol. 472, 137 (1999).
U.S. Pat. No. 6,203,678 issued on Mar. 20, 2001 to Leonhard, et al. discloses a galvanic solid electrolyte sensor for measuring gaseous anhydrides. The sensor includes a ceramic solid electrolyte, a measuring electrode, and a spatially separated reference electrode.
U.S. Pat. No. 5,989,990 issued on Nov. 23, 1999 to Koh, et al., discloses a method for fabricating a tin oxide thin-film sensor using an ion cluster beam deposition (“ICBD”) process.
U.S. Pat. No. 5,525,520 issued on Jun. 11, 1996 to Dinh, discloses a photo-activated, light emitting luminescence sensor and method of detecting trichloroethylene and related volatile organochloride compounds wherein the compounds are directly dissociated by light.
U.S. Pat. No. 5,448,906 issued on Sep. 12, 1995 to Cheung, discloses an ambient temperature, solid state, tin oxide (SnO), or zinc oxide (ZnO) sensor for the detection of oxygen which relies solely upon sorption/desorption.
U.S. Pat. No. 5,275,957 issued on Jan. 4, 1994 to Blades, et al., discloses a method for using TiO2's photocatalytic properties to enhance the disintegration rates of organics in waters.
None of the aforementioned references, however, discloses detecting a deposit, making quantitative determinations with respect to the deposit (i.e., identifying a contaminant and the quantity), “self”-decontaminating the deposit, and determining when chemical decontamination/neutralization is complete.
A need exists in the art for a device and method to detect a substance, make quantitative measurements regarding the substance, detoxify or alter the substance, and indicate when substance (toxic) neutralization is complete. The device and method should perform these functions in real-time or near real-time, so as to facilitate in-situ triage decisions at contaminated sites.